Rotary hydraulic drives



Jan. 9, 1968 E. E. LEWIS 3,362,254

ROTARY HYDRAULIC DRIVES Filed Oct. 5, 1965 [n we nior Ernest E. Lewis By his Attorney United States Patent 3,362,254 ROTARY HYDRAULIC DRIVES Ernest E. Lewis, Topsfield, Mass., assignor to United Shoe Machinery Corporation, Flemington, N.J., a corporation of New Jersey Filed Oct. 5, 1965, Ser. No. 493,135 3 Claims. (Cl. 74-640) ABSTRACT OF THE DISCLOSURE A hydraulic actuator utilizing a circular wave of radial deflection, effected by radial pistons controlled by a rotary valve is made versatile and more effective at different conditions of speed, load, and flow by having another .valve adjustable selectively to maintain and control appropriate back pressure on the pistons during exhaust portions of each cycle.

This invention relates to the provision of a fluid pressure operated rotary actuator, and more especially to an improved hydraulic actuator of the harmonic drive type. It will be appreciated that the invention is not limited to the exemplary embodiment herein shown for purposes of illustration.

In United States Letters Patent No. 3,088,333, granted May 7, 1963,0n an application of C. W. Musser there is disclosed a form ofhydraulic harmonic drive utilizing fluid pressure for. generating in a flex-spline a circumferential wave of radial deflection. As more fully described in the cited patent, for example, a harmonic drive comprises a circular spline and a telescoping flexible spline intermeshing at spaced circumferential points, the sets of spline teeth differing in number, and a wave generator means for progressing the points of spline engagement. The wave generator disclosed in the mentioned Musser patent effects wave progression by means of a series of radially acting pistons operable in proper sequence by a rotary valve.

While that arrangement has been found advantageous in several respects as therein described, it is a primary object of the present invention to provide a greatly improved rotary actuator of the type indicated, having considerably more efficiency and adaptability, and affording smoother performance together with longer wear life.

In accordance with the object just stated, a feature of the present invention resides in the provision, in a harmonic drive of the type having a plurality of cyclically actuated fluid pressure operated pistons for generating a wave in a flexspline, of means for maintaining a small back pressure on the pistons, respectively, during the exhaust portions of their cycles.

The foregoing and other details in construction will now be more particularly described in connection with an illustrative embodiment of the present invention, and with reference to the accompanying drawings thereof, in which;

FIG. 1 is a view in side elevation, largely in axial section, of a hydraulic harmonic drive; and

FIG. 2 is an enlarged section taken on the line I1II of FIG. 1.

FIGS. 1 and 2 largely correspond to FIGS. 1 and 2 of the cited Musser patent for ease of comparison. Refering to FIG. 1 hereof, and assuming a 2-lobe form of wave generation for the sake of simplicity, a stationary housing 20 has secured thereto at one end an annular, internally formed, circular reaction spline .22. Coaxially telescoped Within the circular spline teeth is a flexspline 24, herein shown as cup-shaped, and formed at its open end with external spline teeth 26 (less in number than the circular spline teeth by two or a multiple thereof) adapted upon radial deflection for meshing with the circular spline teeth at diametrically opposite points. These points occur in FIG. 2 on the major axis shown in a vertical position, but it will be understood that, when no fluid operating pressure is applied, the non-deflected flexspline 24 assumes circular condition. FIG. 2 shows the radially deflected, diametrically opposed flexspline teeth along a minor horizontal axis to be disengaged. An output shaft 28 (FIG. 1) is welded to the closed end of the flexspline and suitably journaled in the housing 20. The latter is provided with ports 30 for discharging low pressure fluid such as oil from the hydraulic actuator.

Secured to the opposite end of the housing 20 from the output shaft 28, by bolts 32 extending axially through the circular spline, is a valve housing 34. This housing is formed with a bore 36 coaxial with the circular spline and the flexspline for receiving a rotary valve generally designated 38. It will be understood that the valve 3-8 may be rotated by any desired means such as a motor driven shaft 40 (FIG. 1). A high pressure inlet port 42 in the housing 34 communicates with a chamber 44 located axially between a grooved spool 46 of the valve 38 and its pressure fluid control spool 4-8 about to be described. An outlet port 50 in valve hosuing 34 permits continuous draining of the pressure fluid that leaks past the grooved spool 46 of valve 38. t

The spool 48, as shown in cross section in FIG. 2, is formed externally with diametrically opposed, axially extending channels 51 each of which has one end closed by a plug 52 (one only shown in FIG. 1) and its other end open to the pressurized chamber 44. The circumferential span of each of the channels 51 is s-ufficient to bridge and hence effectively communicate with at least two but not more than three adjacent radial holes 54 in a circular series of such bores formed in the housing 34. Accordingly, at diametrically opposite localities, high pressure fluid is admitted to at least two (but not more than three) adjacent, radial, enlarged cylinders 56 communicating with the respective holes 54 and respectively having a multi-grooved cylindrical piston 58 slidable axially therein. Outer ends only of the novel pistons 58 are spherical but, unlike performance of the Musser pistons which were wholly spherical, are maintained in continuous engagement with the internal surface of an outer flexible ring 60 by means to be explained. As heretofore, the ring 6-0, which is secured by a retainer ring 62 (FIG. 1), is thus elastically deflectable by the radially displaced pistons 58 to impart an ellipsoidal shape to the flexspline, the progressively pressurized piston-cylinders effecting rotation of the shape (and of its major diameter) of the ring 60, and hence of the flexspliue and the output shaft 28.

Advantageously, in contrast to the earlier arrangement wherein only single opposed pistons were pressure actuated simultaneously, the present construction enables a minimum of two opposed pairs of pistons (and a maximum of 6 pistons) adjacent to a major diameter to be operative at one time. This is conducive to materially increased output capability.

Exhaust passageways 64, 64 in the form of circumferentially opposed kerfs in the spool 48 are interconnected by a transverse bore 66 to permit all exhaust fluid to flow (to the left in FIG. 1) through an axial center bore 68. The spool 48 is axially tapped threadedly to receive a pressure relief valve 70 communicating with the bore 68. Preferably the arrangement is such that a piston-type plunger 72 of the valve yieldable axially (to the left in FIG. 1) against resistance of an adjustable return spring 74 is shiftable to its open or exhaust position (shown in dotted lines) when exhaust pressure exceeds a selected minimum value which is normally small relative to operating pressure. The relief valve 70 thus maintains a nominal back pressure across the pistons of the exhausting cylinders. This has been found to improve operating efficiency on the order of over prior units of the same general type hitherto employed. This superior performance is believed due to the fact that the differential or back pressure, not obtainable by installing a pressure relief valve in a housing drain, prevents the pistons from separating from the ring 60 due to inertial effects as they move inwardly from their major axis positions to their minor axis positions. It will be appreciated that, when such piston separation can occur, high fluid pressure must be exerted again on the pistons before they can commence doing useful work.

Improved efliciency is attained by this novel construction too in that the back pressure in the exhaust lines is maintained at a minimum of about 8 atmospheres thereby preventing entrained air from expanding to atmospheric pressure in exhausted cylinders and requiring high pressure oil to compress this volume during the cylinder charging portion of a cycle. In other words, compressibility flow is reduced. Maintenance of contact between the spherical piston ends and the race ring 60 advantageously insures longer wear life by avoiding piston impacts which incidentally cause noise and possible damage.

Having thus described my invention, What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a harmonic drive transmission having a circular spline and a cooperative fiexspline in telescoping relation, a plurality of cyclically actuated, circularly disposed fluid pressure operated pistons for processing a wave of radial deflection in the fiexspline, means for directing fluid under high operative pressure to at least two circnmferentially spaced pistons cyclically and successively, and adjustable valve means for maintaining a predetermined and selectively controlled back pressure on the pistons lower than said high pressure during the exhaust portions of their respective cycles.

2. In a harmonic drive transmission of the fluid pressure operated type having a fiexspline and a circular spline in telescoped relation, a valve housing, a plurality of radially disposed multigrooved cylinder pistons evenly spaced angularly about a bore in the valve housing, said houisng being formed with cylindrical bores for reciprocably receiving said pistons, a deflectable ring bearing on the fiexspline opposite its spline teeth, said pistons having spherical ends arranged and adapted to contact the ring in order radially to displace said spline teeth relative to the circular spline, a rotary valve in said bore having an exhaust port and formed with passages to direct high pressure fluid circumferentially to diametrically opposed ones of the cylinder pistons progressively, and a pressure relief valve mounted for communicating with the exhaust port of the rotary valve and adjustable to insure continuous maintenance of contact with selected pressure between the ring and said piston ends thus to minimize compressibility flow due to entrained air in the operating fluid.

3. A transmission as set forth in claim 2 wherein the rotary valve has a pair of diametrically opposed circumferential channels formed to transmit high pressure input simultaneously to at least two pairs of said cylinder pistons, circumferentially spaced, the remaining pistons of said plurality being connected to exhaust through said cylindrical bores to said pressure relief valve.

References Cited UNITED STATES PATENTS 3,010,435 4/1959 Abrams 91-447 3,086,542 4/1963 Mosier 91447 X 3,088,333 5/ 1963 Musser 74-640 3,128,641 4/1964 Musser 74640 3,151,455 10/1964 Tennis -5-2 DONLEY I. STOCKING, Primary Examiner.

ARTHUR T. MCKEON, Examiner.

J. R. BENEFIEL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,362,254 January 9, 1968 Ernest E. Lewis It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 33, "processing" should read progressing Signed and sealed this 20th day of January 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

